This invention relates to growth factors.
Growth factors play a central role in mediating cell proliferation and differentiation, for example, basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), transforming growth factor-alpha (TGF-.alpha.), and transforming growth factor-beta (TGF-.beta.) have been implicated in the proliferation of connective tissue cells and the induction of angiogenesis characteristic of wound repair (Van Brunt and Klausner, 6 Biotechnology 25, 1988). In addition, Agel et al. (146 J. Pathol. 197, 1985) suggest that growth factors are involved in the etiology of atherosclerosis; for example, the smooth muscle cell (SMC) hyperplasia that accompanies atherosclerosis has been attributed to PDGF, a potent SMC mitogen.
Heparin affinity chromatography has been used extensively for purifying and characterizing a variety of these growth factors. Acidic FGF (aFGF) and basic FGF (bFGF) bind to immobilized heparin columns and are eluted with 1.0M to 1.2M NaCl and 1.5M to 1.8M NaCl, respectively (Folkman and Klagsbrun, 235 Science 442, 1987; Lobb et al., 261 J. Biol. Chem. 1924, 1986). Several growth factors which are structurally homologous to aFGF and bFGF also have an affinity for heparin (see, for example, Rubin et al., 86 Proc. Natl. Acad. Sci. USA 802, 1989). PDGF binds to immobilized heparin, but with relatively low affinity, being eluted with only 0.5M NaCl. Epidermal growth factor (EGF) does not bind heparin to any substantial extent under the conditions described in the cited references on heparin binding growth factors. Lobb et al. (261 J. Biol. Chem. 1924, 1986) report the partial purification by heparin affinity of two classes of growth factors mitogenic for endothelial cells. Gospodarowicz et al. (81 Proc. Natl. Acad. Sci. USA 6963, 1984) report the use of heparin affinity in the purification of bovine brain and pituitary fibroblast growth factors. Shing et al. (29 J. Cell Biochem. 275, 1985) report a chondrosarcoma-derived growth factor purified by heparin-Sepharose affinity chromatography and Bio Rex 70 cation exchange chromatography. Bohlen et al. (185 FEBS Lett. 177, 1985) report a fibroblast growth factor, derived from human brain, which is purified by cation-exchange chromatography, heparin-Sepharose affinity, and reverse-phase HPLC. Shing et al. (223 Science 1296, 1984) report a heparin-binding tumor cell-derived capillary endothelial cell factor. Besner et al. (107 J. Cell Biol. 481a, 1988) report the detection of a heparin-binding, mononuclear cell-derived growth factor(s) which is cationic, is of 6000-14,000 MW, is inactivated by heat (100.degree. C., 10 min), is inactivated by dithiothreitol (5 mM), and is resistant to incubation with 4M guanidine or 0.1M HCl.